In the above formula, \(\mathbf {S_1}\)  and \(\mathbf {S_2}\)  denote the spin of quark and antiquark, respectively. \({L}\)  indicates the orbital momentum between two quarks while \({F}\)  is related to the Gell-Mann matrices in color space. In addition, we take \(\langle {F_1}\cdot {F_2}\rangle =-4/3\)  for meson system.
More details of the MGI model can be found in Ref. [1]}.
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